This invention relates to the field of spectrometry; in particular, it concerns the qualitative and quantitative analysis of sample materials using single beam multiple wavelength analysis method.
Such spectrometers have in the past been based on a scanning device employing a dispersive element, such as a prism or grating, or use of the Fourier Transform-Michelson interferometer to generate a spectrum. A spectrometer introduced in the early 1970's employed a circular variable filter which, upon rotation, generated a complete spectrum from 2.5-14.5 microns utilizing three filter segments. This spectrometer was capable of determining the concentrations of virtually all IR absorption gases over a range of concentration of several percent to 1 part per million. Later this spectrometer was placed under microprocessor control which made measurement and readout possible in all mid-IR wavelengths.
Other filter spectrometers in use in the mid-IR employ discrete filters for the measurement of a particular chemical species, such as hydrocarbon-in-water measured post extraction at 3.4 microns, and carbon dioxide gas at 4.25microns.
These aforementioned spectrometers have one thing in common: they perform a quantitative measurement of a species of chemical, or several measurements of this type. They are not employed to perform qualitative identifications of organic and inorganic molecules, despite the necessity for qualitative identifications in the work of the majority of analytical laboratories and in a broad variety of field analysis needs, such as in the disciplines of geology, materials recycling, archaeology, etc.
In addition, many commercially available spectrometers include filters on a rotating wheel which is moved during each observation period, thus creating a problem of instability as well as the need for large areas of filter material, which raises the cost of such devices.
Accordingly, it is the object of the present invention to provide a multiple wavelength spectrometer of a portable size for use in the field to obtain qualitative identification of all solids, liquids, and gases.
Another object of this invention is to provide such a spectrometer which offers an exceptional signal-to-noise ratio in a very small device, allowing accuracy, stability, and cost-effectiveness. This object is accomplished in the present invention with the use of highly efficient compound parabolic concentrators which produce an exceptional signal-to-noise ratio, and a very stable stationary set of filters.